Many government, industrial, and military systems include devices that are synchronized at different locations. In the absence of clocks that can be transported while remaining exceptionally stable and reliable, synchronization utilizes some sort of timing signal to be transmitted from one location to another. Such signal can be transmitted via a communication channel (e.g., radio, microwave, internet). As long as the time of flight is known, the receiver can synchronize its clock with the sender's clock to within technical uncertainties. In the context of a Global Positioning System (GPS), GPS based timing schemes are based on the concept of synchronization of clocks. GPS receivers obtain signals from multiple satellites and calculate position and time based on the time difference between the signals. Schemes such as GPS are considered vulnerable to: spoofing, in which an adversary replaces a valid timing signal with its own; and interference, in which an adversary provides multiple timing signals, leaving the receiver unable to identify the correct signal. Conventionally encrypted timing signals can mitigate some of these vulnerabilities, but are in many cases impractical to implement.
Conventional infrastructure and associated devices, such as a conventional grid power sub-station, have become increasingly dependent on microprocessor and programmable logic-based monitoring and control systems. Many of these types of conventional infrastructure devices utilize precision timing sources for synchronization of various functions.
For instance, in the context of an electric grid, precision timing may be used across power generation, transmission, and distribution domains. The distribution of timing information across the electric grid is conventionally accomplished primarily through the global positioning system (GPS). The GPS system provides timing information with a resolution, precision, and accuracy utilized by the electric grid to coordinate efforts across domains of a large geographic scale. For instance, timing information may be synchronized for two devices that are 100 kilometers or more apart.
Reliance on the GPS system, however, is not without downsides. The GPS system is generally outside the control of the electric grid or other devices utilizing the system. Further, the GPS system has been shown to be vulnerable to spoofing attacks. The lack of control or the spoofing possibility, or both, mean that reliance on the GPS system can cause adverse effects on operation. In some cases, the timing information may be critical to operation, meaning adverse effects due to spoofing or receipt of signals from the GPS system may cause fault conditions.
Conventional efforts have been made to reduce reliance on the GPS system for timing information. In the case of the electric grid, precision timing protocol (PTP) has been utilized to synchronize clocks of devices on the electric grid. However, conventional PTP, as well as other conventional efforts to reduce reliance on the GPS system, can be susceptible to security and integrity compromises. For this reason, many aspects of the electric grid and devices in other realms utilize the GPS system for timing information despite the lack of control and the spoofing possibility.
With the potential security issues with the conventional time reference and distribution system for the electric grid, the electric grid can be vulnerable to black outs and damage to critical infrastructure. For instance, electrical distribution systems servicing a high density of customers in urban and suburban areas with load densities that can exceed 60 MW and 3 MW per square mile, respectively, can cause significant losses if taken down unexpectedly. Urban distribution centers may comprise sub-stations servicing high loads and separated by distances of several tens of miles or less. Many of these centers are capable of automatic shedding of 300 MW or more. The North American Electric Reliability Council (NERC) considers these assets to be critical because improper shedding of a large amount of power in such a system can damage the electrical power grid.